1. Field of the Invention
The present invention relates to an improved valve support structure for a downhole tool of the type having a spherical valve member which is actuated by longitudinal movement thereof relative to an elongated actuating arm.
2. Description of the Prior Art
During the course of drilling an oil well, one operation which is often performed is to lower a testing string into the well to test the production capabilities of the hydrocarbon-producing underground formations intersected by the well. This testing is accomplished by lowering a string of pipe, commonly referred to as drill pipe, into the well with a formation tester valve attached to the lower end of the string of pipe and oriented in a closed position. A packer is generally attached below the formation tester valve. This string of pipe with the attached testing equipment is generally referred to as a well test string.
Once the test string is lowered to the desired final position, the packer means is set to seal off the annulus between the test string and a well casing, and the formation tester valve is opened to allow the underground formation to produce through the test string.
During the lowering of the test string into the well, it is desirable to be able to pressure-test the string of drill pipe periodically so as to determine whether there is any leakage at the joints between successive stands of drill pipe. To accomplish this drill pipe pressure-testing, the string of drill pipe is filled with a fluid and the lowering of the pipe is periodically stopped. When the lowering of the pipe is stopped, the fluid in the string of drill pipe is pressurized to determine whether there are any leaks in the drill pipe above the formation tester valve.
With the apparatus and methods generally used in the prior art for testing the drill pipe as it is lowered into the well, the fluid in the string of pipe is generally contained within the drill pipe only by the closure of the formation tester valve, i.e., the pressure exerted on the fluid in the drill pipe is also exerted downwardly across the closed formation tester valve.
At other times during the use of a formation tester valve, an upwardly directed pressure differential may be created across the closed tester valve. For example, prior to the opening of the tester valve to test the formation, high formation pressure may build up below the tester valve.
In these and other instances, during the normal use of a formation tester valve or other similar equipment, high pressure differentials both in an upwardly and downwardly direction are periodically imposed across the tester valve.
One particular form of tester valve which has enjoyed widespread usage in the prior art is a full opening type tester valve having a spherical valve element with a full opening valve bore therethrough. The spherical valve element is rotated to selectively open and close the bore of the tester valve by longitudinal movement of the spherical valve member relative to an actuating arm which has lugs engaging eccentric recesses in the spherical valve member.
These various prior art tester valves and related tools utilizing a spherical valve member have generally utilized an assembly wherein the spherical valve member and a pair of annular seats are held together within the tool by C-clamps or a cage member which is in effect hung off an internal part of the tool housing.
With these prior art structures, the spherical valve member has generally been supported against downward pressure differentials only by this clamp or cylindrical cage arrangement suspending the ball within the tool, and thus the high downward pressure differentials across the ball valve have been carried in tension by the clamps or cylindrical cage arrangement.
These prior art arrangements place an inherent limit on the allowable downward pressure differential which can be safely carried by the tool.
An example of the typical prior art arrangement utilizing a plurality of circumferentially spaced C-clamps to suspend the spherical valve member within the tool housing is shown in U.S. Pat. No. 3,814,182 to Giroux. In the structure of the Giroux patent, as best seen with regard to FIG. 1a and FIGS. 8b and 7b thereof, a downward pressure differential across the spherical valve member 5 is carried in tension by the C-clamps 8 and 8a.
Another prior art structure which has provided some improvement over structures like that of Giroux is that shown in U.S. Pat. No. 4,444,267 to Beck wherein the C-clamps of the Giroux type structure have been replaced with an annular elongated cylindrical cage 40 which has an intermediate portion 50 with the lower valve seat 30 cradled therein, and which has a threaded upper portion 52 which is threadedly engaged with an inner upper mandrel 14 of the tool housing. Thus, in the Beck structure, a downwardly directed pressure differential across the spherical valve member 26 is carried in tension by the cylindrical cage 40.
Thus it is seen that although the prior art has recognized the need for an improved support structure for spherical valve members in tools of the type under discussion, there has not been any provision, prior to the present invention, of a structure which supports a spherical valve member in both upward and downward directions against substantially unlimited differential pressures.
Just such an improvement is now provided by the present invention.